System for reproducing sound from a sound record



July 23, 1935. J. H. HAMMOND, JR 2,008,825

SYSTEM FOR REPRODUGING SOUND FROMA SOUND RECORD Filed Oct. 14, 1931 5Sheets-Sheet 1 July 23, 1935. J. H. HAMMOND, JR 2,008,825

I SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD I Filed Oct 14, 1931s Sheets-Sheet 2 July 23, 1935. J. H. HAMMOND, JR

SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD Filed Oct. 14, 1931 5Sheets-Sheet 3 ATTORNEY S Patented July 23, 1935 PATENT. OFFICE SYSTEMFOR BEPBODUCING SOUND FROM A SOUND RECORD John Hays Hammond, In,Gloucester, Mass.

Application October 14, 1931, Serial No. 568,688

17 Claims. (01. 179-100.!)

This invention relates to amplifying systems and provides a system forseparating electrical energy into a plurality of frequency groups andfor amplifying the energy in any or all of the groups in accordance withthe strength of the applied energy in that group. The outputs of thesesystems may be combined and reproduced by a single means, or the outputof each system may be reproduced independently.

The invention provides a method by which various frequency groups may beamplified independently, the amplification or gain ratio being greaterfor strong signals than for weak ones.

signals.

The system may be used in connection with the pickup from a phonographor from a photographic sound record and may also be applied to a pianoin order to accentuate the high frequencies and give them a greaterrange of amplification than the low frequencies.

The construction of a. piano is such that the high notes are produced bythin short strings and therefore have a relatively small amount ofenergy. By using the present system for these notes it is possible toexpand the volume range and to cause the high frequency notes to berelatively stronger when the piano is played forte and weaker when it isplayed pianissimo, thus producing a more balanced effect in the music.

The invention also consists in certain new and original features ofconstruction and combinations of parts hereinafter set forth andclaimed. Although the novel features which are believed to becharacteristic of this invention will be particularly pointed out in theclaims appended hereto, the invention itself, as to its objects andadvantages, the mode of its operation and the manner of its organizationmay be betterunderstood by referring to the following description takenin connection with the accompanying drawgraph.

Fig. 2 illustrates diagrammatically a modified form of the invention.

Fig. 3 is a front elevation partly in section of a piano constructed inaccordance vention.

with thisin- Like reference characters denote like partsin the severalfigures of the drawings.

Inthe following description and in the claims, parts will be identifiedby specific names for convenience, but they are intended to be asgeneric 5 in their application to similar parts as the art will permit.

Referring more particularly to the form of the invention shown in theaccompanying Fig.

1, a phonographic pick-up i0 is connected to one side of a double-poledouble-throw switch II, the other side of which is connected through atransformer 12 to a photoelectric cell l3 of a talking moving pictureprojector. This cell is illuminated by means of a lamp II the light fromwhich 15 is focused by means of a lens 15 through an aperture 15 in anaperture plate 11 upon the sound record of a moving picture film It. Thelight transmitted through this film is then focused by means of a lens15 upon the photoelectric cell 13.

The blades of the switch II are connected through a transformer 21 tothree filter circuits 22, 23, and 24. The circuit 22 is a high passfilter allowing only the high frequency currents to be transmitted. Thefilter 23 is an intermediate pass filter and the filter 24 is a low passfilter. Each of these circuits is connected to the input circuit of aspace discharge means 25, 26 and 21, respectively. In the output circuitof these de- 30 vices are the primaries of three transformers 3|,

32 and 33, the secondaries of which are connected to potentiometer-s 34,35 and 36, respectively. These potentiometers are connected across theinput circuits of three amplifiers 31, 38 and 35 39. The output circuitsof these amplifiers are connected through transformers 4 I, 42 and 43,respectively, to the input circuits of three push-pull amplifiers 44, I5and 4B. The output circuits of these amplifiers are connected throughtrans- 4o formers 41, 48 and 48 to the moving coils of three loudspeakers, 51, 52 and 53. The field windings 54, 55 and 56 of these loudspeakers are energized by suitable sources of power. The three loudspeakers 5], 52 and 53 may be of difierent sizes, each being suitable tothe frequency range which it is to reproduce.

Each of the amplifiers 31, 38 and 39 consists of a space dischargeamplifier 6| in the output circuit of which are the primaries of thetransformers I], I2 and I3. Across the primaries of these transformersare resistances 62. The grid return circuits of the space dischargemeans ii are connected through resistances 63 and batteries 54 to themovable contacts of potentiom- 55 eters 65. The resistances 63 areshunted by condensers 3i and by rectifiers 31, which are in series withthe secondaries of transformers l3. The primaries of these transformersare connected in the plate circuits of space discharge amplifiers II,the grids of which are connected through blocking condensers I2 to theinput circuits of the space discharge devices SI.

In the operation of the form of the invention shown in the accompanyingFig. 1 the switch II is thrown downwhenit isdesiredtousethe phonograph,and is thrown up when it is desired to use the moving picture projector.In either case, the energy received passes through the transformer 2I tothe three filter circuits 22, 23 and 24. These separate out the energyof various frequency groups, the filter 22 allowing the high frequenciesto pass; the filter 23, the intermediate; and the filter 24, the lowfrequencies. These three frequency groups are then amplified by thespace discharge means 25, 23 and 21, the output of which passes throughthe transformers 3I 32 and 33 to the potentiometers 3|, 35 and 33, whereany desired amount of energy from each of the groups may be selected.

The energy from these potentiometers then passes into the input circuitsof the space discharge amplifiers iI of the amplifiers 31, 33 and 33.Parts of these energies pass through he blocking condensers I2 to theinput circuits of the space discharge amplifiers II. The output currentsfrom these amplifiers then pass through the primary windings of thetransformers 53. The currents in the secondaries of these transformersare rectified by the rectifiers 31 and fiow in the direction of thearrows through the resistances 63. This causes potential differences tobe built up across these resistances which are proportional to thecln'rents flowing therein and therefore proportional to the input signalstrength of each of the amplifiers. These potential dif ferences cause adecrease of the biases of the space discharge devices SI, therebydecreasing their impedances and'increasing their amplification ratios.It is thus seen that the amplification or gain ratios of these devicesvary in accordance with the input signal strength, being greater forstrong signals than for weak ones. By making the resistance 53 zero andby reducing the potential of the battery 64 to that for normal bias anyof the stages 31, 33 or 39 may be made to act as normal amplifiers.

The outputs of the space discharge devices 3| pass through the primariesof the transformers I, 42 and I3, and through the resistances 82. Theseresistances are of the order of the internal impedance of the spacedischarge devices GI, and maintain the frequency characteristics ofthese devices independent of the amplitude characteristics. The currentsfrom the secondaries of the transformers II, 32 and 43 are amplified bythe push-pull amplifiers ll, 45 and 46. The amplified outputs from thesedevices then pass through the transformers l1, l3 and 43 to the loudspeakers 5|, 52 and 53, where the high frequency, intermediatefrequency, and low frequency tones are reproduced in the usual manner.

Itisthusseen thatbythissystem the high, intermediate, and low frequencytones are amplified separately, each amplification being accomplished bymeans of amplifiers in which the'amplification or gain ratios vary inaccordance with the input signal strength, being greaterforstrongsignalsthanforweakones. Inthis way, each group of tones isamplified independently and to the best-advantage, each group beingreproduced by a separate loud speaker which is constructed to workmost'eiliciently tage of this system is that by having three separateamplifiers a loud note in any particular frequency group will notcausenotes in the other frequency groups to be amplified out of their trueproportions. In this way it is possible to prevent what is known asblasting, which is caused by one very loud note causing the amplifier toamplify the whole scale instead of that particular note.

Referring to the modified form of the invention Fig. 2 shows anamplifying system which receives its energy from a mechanical pick-upIII, or a photoelectric cell III. This cell receives light from a lampII2 which is energized from a source of power III. The light from thislamp is focused by a lens III through an aperture 5, in an apertureplate IIB, upon the soimd record of the moving film Ill. The light whichpasses through this film then strikes the photoelectric cell III. Thiscell is connected through a transformer II8 to two contacts I2I of adouble-pole double-throw switch I22, the other contacts I23 of which areconnected to the mechanical pick-up III]. The blades of the switch I22are connected to the primary of a transformer I23, the secondary ofwhich is connected to two filter circuits I25 and I26, the former beinga high pass filter, which allows onb the upper harmonics to pass, andthe latter being a low pass filter which allows only low frequencies topass. These filter circuits are connected to the primaries of twotransformers I21 and I23, the secondaries of which are connected topotentiometers I3I and I32, respectively.

The potentiometer I3I is connected in the input circuit of a spacedischarge amplifier I33. The

grid return of said amplifier includes resistance I42 and batteries I31and I38 and is connected to a potentiometer I36. A control amplifier I35is also connected across potentiometer I3I through a stoppage condenserI43. The output circuit of this amplifier I35 is connected through atransformer I 45 to a rectifier circuit including a rectifier I46 andresistance I42. The output circuit of the space discharge means I33 isconnected to the primary of a transformer I" across which is a resistorI48, for thepurpose of keeping the input resistance of the transformerpractically constant and independent of the impedance change between theplate and filament of amplifier I33.

The potentiometer I 32 is connected in the input circuit of a spacedischarge amplifier I5I, the output circuit of which is connected to theprimary of a transformer I52. The secondaries of the transformers I I1and I 52 are in the input circuits of two space discharge means I53 andI, the output circuits of which are connected in parallel to the movingcoil of a loud speaker I55, the field winding I 56 of which is energizedfromasource ofpower I51.

tions from the loud speaker I55 are transmitted In the operation of theform of the invention shown in the accompanying Fig. 2, when it isdesired to use the pick-up IIII the switch I22 is thrown down, and whenit is desired to use the photographic sound record I", the switch I22 isthrown up. In either case, energy is fed to the transformer I24 from thesecondary of which it passes to the two filter circuits I25 and I26. Theformer allows only the high frequencies to pass. The energy from thiscircuit passes through the transformer I21 to the potentiometer I3I,where any desired amount may be fed to the input circuit of the spacedischarge means I33. Some of the energy in thiscircuit passes throughthe stopping condenser I43 to the control amplifier I35. The output fromthis amplifier passes through the transformer I45 and is rectified bythe rectifier I46, causing a D. C. current to flow in the direction ofthe arrow, through the resistor I42. The amount of current flowingthrough this resistor varies the voltage drop therein. Thus, as thiscurrent is increased the potential drop of resistance I42 will beincreased which causes a decrease of the negative potential of the gridof the space discharge amplifier I33 allowing more current to passtherethrough. In this way an increase of amplification for loud signalsis obtained. The energy from the transformer M1 is then amplified by thespace discharge means I53, the output of which passes through the movingcoil of the loud speaker 55, thereby causing the high frequency tones tobe reproduced in this loud speaker. The volume of these tones iscontrolled by the potentiometer I3I and the amplification variesaccording to the strength of the original tones so that theamplification ratio is greater for louder tones than for weak ones.

The low frequencies are passed through the filter I26 and thetransformer I29 to the potentiometer I32. The energy from thispotentiometer is amplified by the space discharge amplifier I5I, theoutput of which passes through the transformer I52 and is applied to thespace discharge amplifier I54, the output of which passes through themoving coil of the loud speaker I55 where it is combined with the outputof the space discharge means I53. Thus the low frequencies arereproduced in the loud speaker I55, the volume being controlled by thepotentiometer I32. These frequencies, however, are amplified by astraight system of amplification so that the tones of high and lowintensities are amplified in the same ratio.

Referring to Fig. 3 a piano I6I is shown which is provided with theusual sound board I62 strings I63 and action I64. Mounted on the crossbracing I65 of the piano is the electric magnetic pickup device H0, suchas that shown in Fig. 2. The armature I66 of this device is secured tothe sound board I62 and the winding is connected to the primary of thetransformer I24 of Fig. 2. Secured to the under surface of the soundboard I62 is the loud speaker I 55 which to the sound board I62, thuscausing a regenerative action and also adding the tonal qualities of thesound board to the reproduced music.

This system is particularly useful as applied to a piano inasmuch as thehigher frequency notes are ordinarily of .relatively low intensity anddo not produce as 'much audible response as the low notes unlessstruck-with greater force. The present system avoids this difiiculty andpermits the notes of the higher register to be amplified in any desiredratio with respect to the lower frequency notes whereby various audibleeffects may be obtained.

Although only a few of the various forms in which this invention may beembodied have been shown herein, it is to be understood that theinvention is not limited to any specific construction, but might beembodied in various forms without departing from the spirit of theinvention or the scope of the appended claims.

What is claimed is:

1. A system for the production of sound from a sound record'comprisingin combination a'sound record, a pick-up device therefor, a receiver ofsound energy, a plurality of paths connecting said pick-up device andreceiver, means in said paths for passing different frequency bands ofthe sound energy, and means in at least one of said paths controlled bythe dynamics of the frequency bands passing through said path forcontrolling the intensity of the sound passed through said path.

2. A system for producing sound from a sound record comprising a pick-updevice, three amplification channels, means for separately selecting thehigh frequency, intermediate frequency and low frequency tones andapplying the selected tones to the respective channels, means forindependently controlling the gain ratio of each of said channels by theaverage intensity of energy passing through the particular channel andmeans for producing sound effects thereby.

3. A system for producing sound from a sound record comprising a pick-updevice, a plurality of amplification channels, means for separatelyselecting the high frequency, intermediate frequency and low frequencytones and applying the selected tones to the respective channels. meanscontrolled by the average input energy of each channel for independentlycontrolling the gain ratio thereof so that the energy range is expandedand means for producing sound effects thereby.

4. A system for producing sound from a sound record comprising a pick-updevice, a plurality of amplification channels, means for separatelyselecting various frequency ranges and applying the selected frequenciesto the respective channels, means controlled by the average input energyin certain of said channels for independently controlling the gain ratiothereof so that the energy ratio of said certain frequency ranges isexpanded and means for producing sound effects in accordance with theenergy of each of said channels.

5. A system for producing sound from a sound record comprising a soundrecord, a pick-up, a pair of amplification channels, filter networksassociated therewith whereby the high and low frequency tones areseparately amplified in said channels, means for varying automaticallythe gainratio only of the high frequency channel in accordance with thestrength of signal therein and means for combining the sound effectsfrom the various channels.

6. In a sound producing system, a piano having a sounding board andstrings, pick-up means for picking up vibrations therefrom, filtercircuits for separating the high and low frequency energy derived fromsaid pick-up means, means for separately amplifying said high and lowfrequency energies and means for controlling the ratio of said energiesto produce the desired sound eifect.

7. In a sound producing system, a piano having a sounding board andstrings, pick-up means for picking up vibrations from said soundingboard, filter circuits for separating the high and low frequency energyderived from said pick-up means, means for separately amplifying saidhigh and low frequency energies, means for va-, rying the amplificationratio of the high frequency energy in accordance with the strength ofsaid energy and means for producing a sound effect by the combinedaction of the high and .low frequency energies.

8. In a phonographic system, a source of sound energy, a receiver ofsound energy, a plurality of paths between said source and saidreceiver, means in said paths for passing different frequency bands ofthe sound energy, and means in at least one of the paths controlled bythe dynamics of the frequency bands passing through said path formodifying the dynamics of the sound passing through that path.-

9. In a sound reproducing system, a sound record, a pick-up devicetherefor, a speaker for delivering sound, a plurality of paths betweensaid pick-up device and said speaker, means in said paths for passingdifferent frequency bands of the sound energy, and means in at least oneof the paths controlled by the dynamics of the fre-- quency bandspassing through said path for expanding the dynamics of the soundpassing through that path. I

10. The method of reproducing a recorded selection from a sound recordwhich comprises picking up the selection from said record, dividing saidselection into different frequency bands and separately expanding thedynamics of at least the highest frequency band.

11. In a phonographic system, the method of reproducing a recordedselection from a sound record which comprises picking up the selectionfrom said record, dividing said selection into different frequency bandsand separately modifying the dynamic contrast between the loud and softnotes of at least one of the frequency bands.

12.Inaphonsraphicsystem,themethodof the dynamics of a selection whichcomprises picking up said'selection, parately modifying the dynamiccontrast between loud and soft notes in each range of the diiferentregisters of the entire audible spectrum and delivering the modifiedselection into an output device.

13. The method of reproducing a recorded sound selection which comprisespicking up said selection, separately expanding the dynamic rangebetween the loud and soft notes of the different registers of the entireaudible spectrum and translating the modified selection into soundwaves.

14. The method of reproducing a recorded sound selection which comprisespicking up said selection, expanding the dynamic range of the higherpitch notes while leaving the dynamic range of the lower pitch notessubstantially unchanged and translating the modified selection intosound waves. a

15. In a phonographic system, the method of improving a sound selectionwhich comprises picking up said selection, modifying the dynamic rangeof a part of the audible spectrum while leaving the dynamic range of therest of the audible spectrum substantially unchanged, and delivering themodified selection into an output device.

16. In a system of amplifying audio frequency signals, means fortranslating a signal from a sound record, a pair of amplifying circuits,filters associated with each of said circuits and connected with saidtranslating means, one of said filters being adapted to pass the highfrequency components of the applied signal and the other of said filtersbeing adapted to pass the low frequency components of the appliedsignal, and means in each of said amplifying circuits controlled inaccordance with the intensity of the signal in said circuit for varyingthe gain ratio of said amplifier whereby the volume ratio of each ofsaid components is expanded.

17. In a sound record system, an originator of sound energy, a receiverfor said sound energy, a plurality of paths connecting said originatorand said receiver, filter means in each of said paths for passingdifferent frequency bands through said paths, an amplifier in each path,and means in each path controlled by variations in intensity of thesound energy in that path for controlling the gain ratio of theamplifier in that path.

. JOHN HAYS HAMMOND, JR.

